Up until now, there has been known a torsional shock absorbing apparatus which is constructed to drivably connect a driving source such as an internal combustion engine, a driving motor and the like with rotation wheels to transmit a rotation torque from the driving source to the rotation wheels, and to absorb torsional vibrations between the driving source and a power transmission train having sets of transmission gears.
The torsional shock absorbing apparatus of this kind is exemplified to comprise a driving rotation member selectively engageable or disengageable from a flywheel forming part of the driving source, a driven rotation member drivably connected with an input shaft forming part of a transmission, and a pair of resilient members having the driving rotation member and the driven rotation member resiliently connected with each other in the circumferential direction (for example see Patent Document 1).
The driving rotation member is constituted by a clutch disc, and a pair of disc plates disposed radially inwardly of the clutch disc, while the driven rotation member is constituted by a hub disposed between the disc plates to be rotated together with the input shaft of the transmission and axially slidable with respect to the input shaft.
The hub has a cylindrical boss splined to the input shaft and a flange extending radially outwardly and formed in a disc-like shape. Each of the resilient members is constituted by a coil spring accommodated in each of windows formed in the flange and has circumferential both ends supported on the ends of the windows respectively formed in the pair of disc plates.
The torsional shock absorbing apparatus thus constructed in the above description is operative to have the clutch disc and the pair of disc plates relatively rotated with the hub, whereupon the coil springs are circumferentially compressed by the relative rotation of the clutch disc and the pair of disc plates with the hub, so that the torsional vibrations inputted from the driving rotation member to the driven rotation member can be absorbed and attenuated by the coil springs.
On the other hand, it is known that the torsional vibrations tend to cause in the transmission noises which occasionally come to be causes for abnormal sounds in the idling operation of the vehicle, abnormal sounds in the travelling operation of the vehicle, and muffled sounds. Therefore, it is required to suitably set the torsional characteristic of the torsional shock absorbing apparatus in order to absorb the torsional vibrations leading to the causes for the abnormal sounds.
Here, it has so far been known that as the abnormal sounds at the time of the idling operation of the vehicle, abnormal sounds called “garagara”, so called, “gara sounds” are caused by the collisions of the idling gear pairs in the no load state of the vehicle forming part of transmission gear sets by the torsion vibrations originated from the rotation fluctuation caused by the torque fluctuation of the internal combustion engine when the vehicle is under the idling operation immediately after being changed to the neutral operation.
On the other hand, it has so far been known that as the abnormal sounds at the time of the travelling operation of the vehicle, abnormal sounds called “jarajara”, so called, “jara sounds” are caused by the collisions of the idling gear pairs of the transmission gear sets by the torsional resonance of the power transmission train and by torsional vibrations originated from the rotation fluctuation caused by the torque fluctuation of the power transmission train when the vehicle is under the acceleration and deceleration operations.
Further, it has so far been known that as muffled sounds, abnormal sounds are caused in the vehicle room by the vibrations caused by the torsional resonance of the power transmission train originated from the torque fluctuation of the power transmission train. The torsional resonance of the power transmission train is usually caused under the usual travelling state (for example around 2500 rpm of the rotation number of the internal combustion engine), thereby resulting in generating the muffled sounds in the usual travelling state.
Conventionally, there have so far been known a torsional shock absorbing apparatus disclosed in for example Patent Document 2 as a torsional shock absorbing apparatus having a torsional characteristic suitably set. The known torsional shock absorbing apparatus comprises a cylindrical boss constituting a driven rotation member, and a disc-like flange radially outwardly from the boss, the boss and the flange being divided into two respective sections. Between the outer peripheral portion of the boss and the inner peripheral portion of the flange is disposed a small coil spring having a small spring constant to absorb the torsional vibrations.
A pair of disc plates has first widow portions and second widow portions respectively formed therein, the first widow portions and the second window portions being spaced apart from each other in the circumferential direction of the disc plates. The flange is formed with a first window and a second window which are in opposing relationship with the first window portions and the second window portions of the disc plates. In the first windows of the disc plates and the first windows of the flange are accommodated first coil springs, and first seat members, respectively, each of the first coil springs having a spring constant larger than the small coil spring.
In the second windows of the disc plates and the second windows of the flange are accommodated second coil springs, and second seat members, respectively, each of the second coil springs having a spring constant larger than the small coil spring.
The first sheet member has a gap circumferentially extending from the first window portion, and the first coil spring is not compressed in the area where the torsional angle is small when the second coil spring is compressed, and the first coil spring is compressed in the area where the torsional angle is large.
The torsional characteristic of the driving rotation member and the driven rotation member in the torsional shock absorbing apparatus is shown in FIG. 11.
In the area where the torsion angle of the clutch disc and the hub is small as in the state that the vehicle under the idling operation is changed to the neutral operation, the torsional shock absorbing apparatus is operative to have only the small coil spring compressed, thereby suppressing the “gara sound” by lowering the rigidity of the torsional characteristic in the small torsion angle area.
On the other hand, in the large torsion angle, only the second torsion spring is compressed to obtain the intermediate rigidity of the torsional characteristic with the torque being slowly raised as shown by a reference symbol “a” in FIG. 11, thereby making it possible to suppress the muffled sound.
When the torsion angle is further increased to the predetermined level, the first coil spring and the second coil spring are concurrently compressed to obtain the high rigidity of the torsional characteristic with the torque increase ratio being raised as shown by a reference symbol “b” in FIG. 11, thereby making it possible to suppress the “jara sound” sound. In this way, the multi-staged torsional characteristic can be obtained.
The conventional torsional shock absorbing apparatus thus constructed, however, encounters such a problem that in the stepped portion (bent portion in the graph) with the transmission torque increase ratio being varied, there is caused gear colliding sounds of the gears transmitting the rotation torque in the transmission.
The sound thus caused has a low frequency which is called “ga sound”. When the torque transmitted from the driving rotation member to the driven member is about zero degree and an abrupt fluctuation is caused at the stepped portion of the torsional characteristic for example at the time of the slow deceleration travelling of the vehicle, the conventional torsional shock absorbing apparatus also encounters such a problem that there are caused abnormal sounds such as gear colliding sounds caused by the rebound of the gears and other noisy sounds.
In view of this problem, another torsional shock absorbing apparatus is proposed and disclosed in the Patent Document 3 as a torsional shock absorbing apparatus which can suppress the “ga sound” by making the torsional characteristic in non-linear shape with no multi-stages to have the torsional characteristic formed with no stepped portion of the torque fluctuation.
The torsional shock absorbing apparatus disclosed in the Patent Document 3 comprises a driving rotation member integrally with an internal combustion engine, a driven rotation member disposed in coaxial relationship with and in relative rotational relationship with the driving rotation member, a displacement member having a contact portion movable along a contacted surface formed to have a curvature varied in response to the relative rotation angle of the driving rotation member and the driven rotation member, and relatively displaceable with respect to the driven rotation member with the contact portion being movable along the contacted surface in response to the relative rotation angle of the driving rotation member, a resilient member resiliently compressed and expanded in response to the relative displacement of the displacement member, and stopper portions respectively provided on the driving rotation member and the displacement member and held in engagement with each other to regulate the relative rotation of the driving rotation member and the displacement member and thus to regulate the relative rotation of the driving rotation member and the driven rotation member.